A sheet post-processing apparatus for performing post-processing on sheets conveyed from an image forming apparatus (for example, a multi-function peripheral (MFP)) is known. The sheet post-processing apparatus includes a processor for stapling or sorting the conveyed sheets. The sheet post-processing apparatus further includes a sheet discharge tray and a drive motor. The sheet discharge tray can stack sheets discharged from the processor. The drive motor raises and lowers the sheet discharge tray. The sheet discharge tray is driven to be raised and lowered in a state in which a large number of sheets are stacked (hereinafter also referred to as a “high load state”). The sheet discharge tray is required to be driven at a high speed in the high load state.
On the other hand, there is a mechanism that provides a reverse load to the sheet discharge tray in a reverse direction to the load generated on the sheet discharge tray.
For example, there is a mechanism that provides a reverse load to the sheet discharge tray by pulling the sheet discharge tray with a force-applying unit such as a tension spring. The reverse load serves as assistance for the drive motor.
On the other hand, when there is an obstacle below the sheet discharge tray, it is necessary to prevent the sheet discharge tray from being pinched by the obstacle.
However, in the mechanism described above, there is room for improvement in addition to achieving miniaturization of the drive motor and prevention of the sheet discharge tray from being pinched by an obstacle thereunder.